In the related art, a rail plug is known in which the principle of a rail gun is utilized to move plasma (or a spark discharge) by a Lorentz force into a combustion chamber, to thereby improve ignition in the combustion chamber. FIGS. 14 and 15 are diagrams showing such a rail plug 100. As shown in FIG. 14, the rail plug 100 comprises two electrodes 1 and 2 which are placed in parallel to each other with a gap 3 therebetween. Here, an example configuration is shown in which the electrode 1 is an anode and the electrode 2 is a cathode.
A voltage is applied between the two electrodes 1 and 2, to generate plasma P in the gap 3 between the electrodes 1 and 2. A discharge path 4 in which a current flows from the electrode 1 to the electrode 2 is formed by the plasma P. A Lorentz force F acts on the discharge path 4 due to the current flowing therein. FIG. 15 shows the principle of action of the Lorentz force F when a current flows in a conductor. As shown in FIG. 15, a magnetic field B is formed between a magnet M1 having a polarity of N and a magnet M2 having a polarity of S and placed opposing the magnet M1, and a direction of a magnetic field vector in the magnetic field B is from the magnet M1 to the magnet M2. Here, a direction of the current flow, a direction of the magnetic field, and a direction of the Lorentz force are in an orthogonal relationship with each other.
When a current I flows from a deeper side of the page of FIG. 15 toward the front side in a conductor D placed in the magnetic field B, according to Fleming's left-hand rule, a Lorenz force F directed to the right side in FIG. 15 acts on the conductor D. The Lorentz force F in this case is represented by F=(I×B)L, Here, L represents a length of the conductor D in the magnetic field B.
Referring back to FIG. 14, by causing such Lorentz force F to act on the plasma P generated between the electrodes 1 and 2, it is possible to set the plasma P as a shell P1 and to move the shell P1 from the gap 3 between the electrodes 1 and 2 into the combustion chamber, to thereby improve ignition in the combustion chamber.
JP 2010-203295 A discloses a technique in which a direction of plasma ejected into the combustion chamber is changed by the Lorentz force, to avoid concentrated use of particular positions of a central electrode and a grounding electrode for in-gas discharge, to thereby prevent rapid wear of the electrodes.
FIG. 16A is a graph showing a relationship between a time from start of discharge (ms) and a discharge current (A) in the rail plug 100 described above with reference to FIG. 14. FIG. 16B is a graph showing a relationship between the time from the start of discharge (ms) and a plasma length (mm) in the rail plug 100. As shown in FIG. 16A, as an inductance L1 of the conductor is increased, the discharge current is reduced and the plasma length tends to be elongated.
However, in the rail plug 100, because the magnetic field B for causing the Lorentz force F for acting on the plasma P is formed by the current flowing in the electrodes 1 and 2 themselves, a current of 50 A˜200 A is required, as shown in FIG. 16A. Therefore, when the plasma P is repeatedly generated with such a large current, disadvantages may be caused such as melting of the electrodes 1 and 2. In addition, such a structure cannot be used for an application in which the plasma is generated with a relatively low current (for example, 100 mA), such as, for example, an ignition plug for an internal combustion engine for a vehicle.
An advantage of the present disclosure lies in provision of an ignition device for an internal combustion engine, which can improve ignition while reducing power consumption.